Okay, first of all I'm not going to ban CozyCreature12, for the simple reason that they already left the conversation two days ago and didn't keep pushing it.
However, I will require them to stop posting in bi-related discussions from now on. If you've got a problem with bi people, that's your problem and you need to keep it to yourself. If you do post in those discussions, that will be grounds for a ban, just so they understand.
As to bisexual people in manga, it's a huge failing on the part of manga authors in general that they keep writing them so badly. Because of that, I can understand people not wanting to read stories with a bisexual tag because more often than not they're full of bi-phobic tropes, whether intentional or not. If anything, this particular story is an exception to the rule in that the bisexual character is actually a pretty decent person who's not unfaithful, predatory, or what have you. So calling it toxic because it contains bisexuality is ridiculous and so is anyone who says it is.